As one of electrically erasable programmable read-only memories (EEPROMs), a NAND flash memory is known. NAND flash memories are used as various recording media including a file memory and memory card.
A memory system including the NAND flash memory is configured to further include, for example, a controller, and random access memory (RAM) used for storing temporary data. In the NAND flash memory, although various data items necessary for the controller to operate are stored, reading data from the NAND flash memory each time the data is used takes much time. Accordingly, for example, data once read from the NAND flash memory is stored in a RAM, and the controller uses the data stored in the RAM to operate the system.
Power consumption of the RAM is large, and hence it is conceivable that the power supply for the RAM is turned off for the purpose of reducing the consumption current when there is no access to the RAM. However, when the power supply of the RAM is turned off, data items stored in the RAM are erased, and hence when the power supply of the RAM is turned on, the need to reload necessary data from the NAND flash memory arises. In order to load data from the NAND flash memory, although it is necessary to access the NAND flash memory to carry out page read, page read of the NAND flash memory takes much time, and the consumption current thereof is not small.
It should be noted that in Jpn. Pat. Appln. KOKAI Publication No. 2008-108026, a technique for reducing the capacity of a battery necessary for the backup for a cache memory in a storage system provided with a volatile cache memory is disclosed.